Agreed. I NEVER use zebras to set exposure based on skin tones. Never. In my opinion, anyone who does that is ultimately just guessing at the right exposure because, as Leonard and Brian would agree, everyone's skin tone is different. 70% might be perfect for one person, and 60% might be right for someone else because they are a different race or just got back from a sunny vacation. Obviously an experienced operator can still get acceptable results, but in my opinion, ultimately they are just using intuition and guessing at the exposure -- especially if they can be a little sloppy because they know they're going to grade in post. I spend a lot of time teaching other people how to shoot, and I can't teach intuition and gut feelings. I prefer to show beginners how to be more precise and consistent with their exposure and nail it perfectly at the time of the shoot. It's not rocket science. Therefore, I have my zebras setup to measure bright white and/or an 18% gray card. Those are the only two things that I count on to be consistent. Trusting zebras on almost anything else (except a chip chart) is ultimately just guessing.

Quote: "Also my experience is that sometimes video is simply not linear."

Leonard, once again I totally agree and this is a point I demonstrate in my F3 training DVD. The difference in sensitivity between two cameras with different paint settings might be 1-stop in middle grays, and 2-stops in the highlights. How does a light meter take that into consideration? It can't.

Exactly Doug, though in my experience I find zebras on flesh tones very useful, but like everything else its a guide only for run and gun work and then I keep them at 60% for caucasian skin and then just try to wing it using my judgement.
Nothing beats a reliable monitor and waveform.